Process for activating aluminum containing anode and anode



2 Sheets-Sheet 1 M. J. PRYOR PROCESS FOR AG'IIVATING ALUMINUM CONTAININGANODE AND ANODE Dn V 3 3 mm mm 9 m M E mR m 8 WP n m m M M ms E H A H 8m M 24 we 9 m w 3 w w. Q a w 8 m 05 2 Q32 Q52? wm fi m6 A V M as B GN3 s.3 0 w 6513? 3% 3 2 Jan. 11, 1966 Filed June 6, 1963 characteristics.

United States Patent T 3,228,866 PROCESS FOR ACTIVATING ALUMINUM CON-TAINING ANODE AND ANODE Michael J. Pryor, Hamden, C0nn., assignor toOlin Mathieson Chemical Corporation Filed June 6, 1963, Ser. No. 286,05612 Claims. (Cl. 204197) The present invention relates to a process foractivating aluminum-containing anodes and to the improvedaluminum-containing anode thereby obtained.

Because of their numerous excellent properties, aluminum-containinganodes have been Widely used in a variety of applications, for example,aluminum-containing anodes may be advantageously used (1) in primaryelectric batteries suitable for use with liquid electrolytes, such asaqueous electrolytes and especially sea water, (2) as sacrificialaluminum-containing anodes in conjunction with a metallic cathode whichthereby receives substantial protection against corrosion and '(3) inprimary cells of the dry type, with the aluminum-containing anode alsoserving as the container for the cell.

Particularly advantageous are the numerous aluminum base alloysespecially formulated to provide good anodic Examples of suchaluminum-containing alloys may be found in United States patentapplication Serial No. 251,024, filed January 14, 1963, now Patent No.3,789,486, which relates to a highly efiicient metal anode comprising analuminum base alloy containing at least 90 percent aluminum and between0.04 and 0.5 percent tin.

One disadvantage, however, of aluminum-containing anodes which haslimited their effectiveness for numerous applications is the relativelylong periods of time required for these anodes to achieve full poweroutput. For example, the aluminum-tin alloys disclosed in United Statespatent application Serial No. 251,024, referred to above, achieve fullpower output after approximately one minutes operation. Thisdisadvantage is especially significant when aluminum-containing alloysare utilized as the anodes of sea water batteries containing, forexample silver chloride cathodes. These batteries are activated byfilling with sea water and must achieve full power output in a matter ofseconds, especially in view of relatively short life of the battery,often as little as six minutes.

The magnesium alloys conventionally used as anodes in sea waterbatteries generally achieve full power output after approximately 15seconds. However, the aluminum-containing anodes have numerous highlydesirable advantages over the magnesium anodes and, therefore, it ishighly desirable to simply and conveniently overcome the foregoingdisadvantage, namely, the relatively slow activation characteristics ofaluminum-containing anodes.

The relatively slow activation rate of aluminum-containing anodes isbelieved to be due to the surface oxide and hydrated oxide corrosionproducts that form on the anodes during standing in ordinary air.Abrasive removal of the corrosion products is effective in increasingthe activation rate; however, the corrosion products quickly reformswhen the aluminum surface is allowed to remain in air, even, forexample, after 24 hours in a desiccator.

It is therefore, an object of the present invention to provide a processfor activating aluminum-containing anodes and to provide an improvedanode.

It is a further object of the present invention to provide an improvedaluminum-containing anode, and an improved process for obtaining same,said anode being characterized by rapid achievement of full poweroutput.

It is a still further object of the present invention to provide animproved process and an improved anode as 3,228,866 Patented Jan. 11,1966 above without impairing the other desirable characteristics of theanode.

Further objects and advantages of the present invention will appearhereinafter.

In accordance with the present invention it has been now found that theforegoing objects and advantages may be readily obtained and a processfor activating aluminum-containing anodes or aluminous anodes providedwhich comprises contacting said anodes, preferably in the substantiallyfilm free condition, i.e., having an average oxide film thickness ofless than 10 Angstrom units, for at least 5 seconds with a diluteaqueous solution of a fatty acid, or preferably a dilute aqueoussolution of a metallic soap, said solution having a pH of from 4 to 7and containing at least 0.1 milligram of soluble fatty acid per liter orcontaining at least 0.1 milligram of the metallic component of a solublemetallic soap per liter. The improved, activated anode of the presentinvention comprises an aluminous anode coated with the foregoing diluteaqueous solution.

In accordance with the process of the present invention it has beensurprisingly found that the simple and expeditious process outlinedabove overcomes the disadvantages in the use of aluminum-containinganodes and achieves full power output in as little as, for example, 15seconds. Especially surprising and unexpected in ac cordance with thepresent invention is that the aluminumcontaining anode treated inaccordance with the present invention actually attains considerablyimproved current density and power output.

The process of the present invention is effective in improving theanodic characteristics of any aluminum base alloy. The criticalrequirement is that the alloy contain a major proportion of aluminum,i.e., greater than 50 percent aluminum, since the aluminum is the factorwhich retard the rapid attainment of full power output. Exemplificativeanodic materials include, but are not limited to, pure aluminum,aluminum base alloys containing varying proportions of alloyingingredients, such as, for example, up to 10 percent zinc to obtainimproved galvanic activity, e.g., alloy 7072 and also, for example,aluminum base alloys containing at least percent aluminum and from 0.04to 0.5 percent tin as discussed in United States patent applicationSerial No. 251,024. Preferably, the tin is retained in solid solution tothe maximum degree, i.e., about 0.1 per-cent, with the excess tin, or asuit-able third ingredient, being provided as taught in co-pendingapplication Serial No. 60,166, filed October 3, 1960, now Patent No.3,180,728, to improve uniformity of corrosion and to improve anodicefficiency.

The preferred manner of preparing the alloys in the above-identifiedco-pending patent applications is to heat the aluminum-tin sample atelevated temperatures, e.g., between about 570-640 C., for a sufficientperiod of time to dissolve the maximum amount of tin and to redistributeexcess tin or other alloying additions in a coarse, particulate formwhich produces maximum uniformity of attack and power efiiciency.Generally, the heating period within the preferred temperature range mayvary between 15 minutes and 24 hours. After the heating period thesample is cooled rapidly, for example, by immersion in a large volume ofwater at ambient temperatures. For simplicity, this treatment may betermed homogenization treatment.

It is preferred in accordance with the process of the present inventionthat the treatment of the aluminumcontaining anode be performed when theanode is in a substantially oxide free state. This is not essential butit has been found that greater improvement is thereby obtained.

The pre-existing, heavier oxide coating can be removed by conventionalmeans, for example, etching or mechanical abrasion or wire brushing,preferably the mechanical abrasion is performed under the contactingsolution so as to avoid the reformation of oxide coatings having athickness of greater than 10 Angstroms. Similarly, if etching isemployed or prior mechanical treatments, it is desirable to avoidsubsequent formation of excessive oxide coatings.

The process of the present invention comprises contacting the aboveanode for at least 5 seconds with a dilute aqueous solution of ametallic soap or of a fatty acid. Longer contact times may be preferredto obtain maximum exposure, for example, on the order of 5 to 60minutes. Extended contact times may be used, if desired, but excessivecontact times are not beneficial. The solution should have a pH of from4 to 7 and contain at least 0.1 milligram of the metallic component ofthe soluble metallic soap per liter or of soluble fatty acid per liter.Generally up to 10 milligrams per liter may be employed, preferablyaround 1.0 milligram per liter. While the metallic soaps are preferredin accordance with the present invention, the fatty acids themselves maybe conveniently used. The particular method of contacting the anode withthe solution is not critical and any convenient method may be employed,for example, immersion, spraying, brushing, coating, etc.

The term metallic soap is used in its conventional sense to contemplatethe salts of heavy metals with oleic, stearic, palmitic, erucic,recinoleic, pelargonic, suberic, azelaic and lauric acids, for example,and more generally the salts of long chain fatty acids with the heaviermetals, such as cadmium, copper, lead, tin or zinc. Representativemetallic soaps include, but are not limited to, the salts of theforegoing heavy metals with the foregoing acids. Generally, it ispreferred to use the long chain fatty acids which contain one or moreunsaturated bonds. The preferred metals are those whose hydroxides arevery weak bases, i.e., with dissociation constants lower than 10- at 25C.

Any fatty acid may be conveniently employed and preferably the longchain fatty acids. A representative list of typical and preferred fattyacids includes, but is not limited to, any of the foregoing fatty acids.

The process of the present invention will be more readily apparent froma consideration of the following illustrative examples.

Example 1 This example represents the typical activation characteristicsof the conventional magnesium alloy AZ 61, a magnesium alloy containingabout 6 percent aluminum, 1 percent tin, 0.3 percent manganese and thebalance magnesium.

The test primary cell was constructed in the conventional manner. Theanodes were shaped from sheet material, generally about 0.02 inch thick.The cathodes Were shaped from silver chloride sheet about 0.015 inchthick. The cathodes Were modified to incorporate insulating spacerswhich would allow them to be placed in close proximity to the anodeswithout electrical short circuiting. This was done, in one of theconventional art manners, by using glass beads fastened to one side ofthe sheet. A multiplicity of holes was drilled in the cathode toincrease the reactive surface of the silver chloride. In addition, thesilver chloride was partially reduced to silver in a conventional mannerby immersion in a photographic film developer.

The electrical contact with the silver chloride cathode was furnished bya 0.001 inch thick 99.9 percent pure silver foil held in pressurecontact in the conventional fashion. External electrical connectionswere made to the anode and cathode, suitably insulated from each otherand from the electrolyte. The anode, cathode and spacers were then tapedtogether to complete the cell structure.

Provisions were made for collecting and measuring hydrogen gas evolvedduring the reaction time, for measuring temperature rise in theelectrolyte and for measuring the potential on open or closed circuit,the current on short circuit (negligible resistance) or with anysuitable simulated load resistance.

In this example the anodic material was the magnesium alloy AZ 61 withno surface pretreatment. The results are shown in the graph of FIGURE 1which shows that full current output from the untreated magnesium alloyAZ 61 was obtained after about 15 seconds.

Example 2 Example 1 was repeated using an aluminum-0.3 percent tin alloyas the anodic material. The aluminum used was at least 99.995 percentpure and the alloying addition was pure tin. When analyzed after castingthis alloy contained 0.30 percent tin and 0.0028 percent iron and lessthan 0.001 percent each of silicon and copper.

The ingot was given a homogenization heat treatment of about 620 C. forfour hours, quenching in water, cold rolled from 0.025" gage to .01"gage and stretched to 0.1 percent of the proportional limit.

The activation characteristics of this alloy are shown in the graph ofFIGURE 1. This shows that full current was not achieved until about oneminute had elapsed.

Example 3 Example 2 was repeated with the exception that thealuminum-tin alloy was abraded for 30 seconds under a 1.0 M sodiumsilicate solution followed by quenching in cold distilled water andimmediately introducing the pretreated specimen into the silver chloridecell. The abrading procedure comprised abrading under the contactingsolution with finely divided (300 mesh) alumina powder contained in astream of argon at a pressure of 50 p.s.i.

The results are shown in the graph of FIGURE 1. It will be seen that thesodium silicate, far from improving the activation time of thealuminum-tin alloy, roughly doubled the time required to obtain aconstant current output in this cell.

Example 4 Example 3 was repeated using a 1.0 M of sodium chromateinstead of sodium silicate. Similar disadvantageous results wereobtained.

Example 5 Lead linoleate extract was prepared by digesting solidtechnical grade lead linoleate with xylene, coating the inside of alarge beaker thinly and allowing the beaker to stand for 8 days topermit the lead linoleate to dry and filling the beaker with deionizeddistilled water to extract a certain quantity of the lead linoleate inaqueous solution over a period of 8 days. Generally amounts of lead onthe order of 200 milligrams per liter were found in the water after thistreatment. The pH of the aqueous extract generally was between 5 and5.5.

Example 6 Example 3 was repeated with the aluminum-tin alloy abraded asin Example 3 under the lead linoleate extract of Example 5 diluted toproduce a concentration of 1.0 milligram of lead per liter. Thespecimens were removed from the aqueous extract, blown dry withcompressed air and stored for 2 days in a desiccator to simulate some ofthe conditions found during natural storage. The activationcharacteristics of the aluminum-tin alloy so treated is shown in FIGURE2 in comparison with that of the magnesium alloy AZ 61 of Example 1.

It will be seen that this activation time of the aluminumtin compositionis reduced to about 15 seconds and is now superior to that of themagnesium alloy AZ 61. Furthermore, surface pretreatment with the leadlinoleate extract not only improved the activation time but alsoimproves the current density so that the treated alloy generates asubstantially higher constant current output than similar un treatedaluminum-tin alloys or the magnesium alloy AZ 61 in the untreatedcondition. After two minutes operation the current output of the leadlinoleate treated aluminumtin sample is still about 7 percent superiorto that obtained in a similar magnesium-silver chloride cell.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiment is therefore to be considered as in allrespects illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, and all changes which comewithin the meaning and range of equivalency are intended to be embracedtherein.

What is claimed is:

1. A process for activating an aluminous'anode which comprisescontacting said anode for at least 5 seconds with a dilute aqueoussolution of a long chain fatty acid, said solution having a pH of from 4to 7 and containing at least 0.1 milligram of soluble fatty acid perliter.

2. A process for activating an aluminous anode which comprisescontacting said anode for at least 5 seconds with a dilute aqueoussolution of a metallic soap, said solution having a pH of from 4 to 7and containing at least 0.1 milligram of the metallic component of asoluble metallic soap per liter.

3. A process for activating an aluminum anode of an aluminum base alloywhich comprises contacting a substantially oxide free aluminum anode ofan aluminum base alloy for at least 5 seconds with a dilute aqueoussolution of a metallic soap, said solution having a pH of from 4 to 7and containing at least 0.1 milligram of the metallic component of asoluble metallic soap per liter.

4. A process for activating an aluminum anode which comprises providingan aluminum anode comprising an aluminum base alloy containing at least90 percent aluminum and between 0.04 and 0.5 percent tin, contactingsaid anode for at least 5 seconds with a dilute aqueous solution of ametallic soap, said solution having a pH of from 4 to 7 and containingat least 0.1 milligram of the metallic component of a soluble metallicsoap per liter.

5. A process for activating an aluminous anode which comprisescontacting said anode for from 5 to minutes with a dilute aqueoussolution of a metallic soap, said solution having a pH of from 4 to 7and containing from 0.1 to 10 milligrams of soluble fatty acid perliter.

6. A process according to claim 2 wherein said metallic soap is leadlinoleate.

7. An activated anode which comprises an aluminous anode coated with adilute aqueous solution of a long chain fatty acid, said solution havinga pH of from 4 to 7 and containing at least 0.1 milligram of solublefatty acid per liter.

8. An activated anode which comprises an aluminous anode coated with adilute aqueous solution of a metallic soap, said solution having a pH offrom 4 to 7 and containing at least 0.1 milligram of the metalliccomponent of a soluble metallic soap per liter.

9. An anode according to claim 8 wherein said aluminous anode is in thesubstantially oxide free state.

10. An anode according to claim 8 wherein said aluminous anode comprisesan aluminum base alloy containing at least percent aluminum and between0.04 and 0.5 percent tin.

11. An anode according to claim 8 wherein said coat ing contains between0.1 and 10 milligrams of said metallic component of a soluble metallicsoap per liter.

12. An anode according to claim 8 wherein said metallic soap is leadlinoleate.

No references cited.

WINSTON A. DOUGLAS, Primary Examiner.

NEWMAN P. BULLOCH, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,228,866 January 11, 1966 Michael J. Pryor fied that error appears inthe above numbered pat- It is hereby certi on and that the said LettersPatent should read as ent requiring correcti corrected below.

Column 1, line 28, for "3,789,486" read 3,189,486

Signed and sealed this 6th day of December 1966.

( L) Attest:

EDWARD J. BRENNER ERNEST W. SW'IDER Attesting Officer Commissioner ofPatents

7. AN ACTIVATED ANODE WHICH COMPRISES AN ALUMINOUS ANODE COATED WITH ADILUTE AQUEOUS SOLUTION OF A LONG CHAIN FATTY ACID, SAID SOLUTION HAVINGA PH OF FROM 4 TO 7 AND CONTAINING AT LEAST 0.1 MILLIGRAM OF SOLUBLEFATTY ACID PER LITER.
 8. AN ACTIVATED ANODE WHICH COMPRISES AN ALUMINOUSANODE COATED WITH A DILUTE AQUEOUS SOLUTION OF A METALLIC SOAP, SAIDSOLUTION HAVING A PH OF FROM 4 TO 7 AND CON-